1) Field of the Invention
The invention relates to polymers and to a positive- or negative-working radiation-sensitive mixture including a binder which is insoluble in water, but soluble or at least swellable in aqueous-alkaline solution, and at least one radiation-sensitive compound. The invention furthermore relates to a recording material having a support and a radiation-sensitive layer, and to a process for the production of chemical-resistant relief recordings in which the recording material is exposed imagewise and then developed using an aqueous-alkaline solution.
2) Description of Related Art
Radiation-sensitive, positive- or negative-working mixtures which are fixed using aqueous-alkaline developers after irradiation are known and have been described for a variety of uses, for example, for the production of copying layers on planographic printing plates. The term "copying layer" is used here and below for a radiation-sensitive layer which has been exposed imagewise and developed, and possibly also baked.
The properties of such copying layers are determined essentially by the binder, in particular since it generally makes up the largest proportion of the total weight of all nonvolatile constituents of the radiation- or light-sensitive mixture. The binders used for positive copying layers are usually phenol-formaldehyde or cresol-formaldehyde condensation products of the novolak type, while negative copying layers based on diazonium salt polycondensates frequently use substituted polyvinyl butyrals. By contrast, layers based on photopolymers frequently use acrylate copolymers of suitable acidity.
However, the properties of the known positive and negative copying layers are not ideal for all applications. In planographic printing plates, the layer is in many cases insufficiently stable to achieve a long print run. In addition, the copying layers of the printing plates are frequently not sufficiently resistant to washing and cleaning media. In particular, in printing from positive copying layers using printing inks which harden in UV light, wash-out agents are used which have a high content of organic solvents (such as ethers, esters or ketones) or are even formulated entirely on the basis of organic solvents. The wash-out agents may cause considerable damage to the copying layer. If novolaks are present as binder, it is imperative to harden the copying layer thermally at temperatures above 200.degree. C. before printing with the abovementioned inks or if a print run of greater than 100,000 prints is to be achieved.
Although negative copying layers based on diazonium polycondensates with polyvinylbutyral binders have significantly better stability to solvents than positive copying layers, the stability to isopropanol attack and similar damping solution additives is, however, usually inadequate. Furthermore, a comparatively high content of organic solvents is necessary in the developer in order to achieve satisfactory delamination.
In negative, photopolymer-based copying layers, the conventional binders are not hard enough to achieve optimum print run performance.
Various binders having an improved property profile have already been proposed. For example, alkali-soluble binders that have been described are phenolic resins based on naphthol, homopolymers and copolymers of vinyl-phenols (DE-A 23 22 230=U.S. Pat. No. 3,869,292, DE-A 34 06 927=U.S. Pat. No. 4,678,737), homopolymers and copolymers of hydroxyphenyl (meth)acrylates (JP-A 51 36129), dihydroxyphenyl (meth)acrylates, hydroxynaphthyl (meth)acrylates, hydroxybenzyl (meth)acrylates, hydroxyphenyl(meth)acrylamides (JP-A 50-55406), hydroxybenzyl(meth)acrylamides (DE-A 38 20 699=U.S. Pat. No. 5,068,163) or hydroxynaphthyl(meth)acrylamides, and copolymers of hydroxyphenylmaleimides (EP-A 0 187 517). Known alkali-soluble binders in radiation-sensitive mixtures also include homopolymers and copolymers containing halomethyl units and homopolymers and copolymers of monomers containing NH-acidic groups, for example, made from N-methacryl-sulfonamides (DE-A 37 42 387) or from sulfamoylphenyl (meth)acrylates or N-sulfamoylphenyl(meth)acrylamides (EP-A 0 330 239 and EP-A 0 544 264).
With the exception of the above polymers containing hydroxyphenylacrylamide units or with units containing NH-acidic groups, none of said binders has hitherto been used practically. The reasons for this are the poor development behavior, excessive developer consumption, impairment of the exposure contrast and complex preparation of the monomers. Binders containing hydroxyphenylacrylamide units are furthermore not sufficiently resistant to solvent-based cleaning agents and damping solutions. Binders containing NH-acidic groups are not sufficiently stable, even after thermal treatment, to allow a long print run.